A vision system checks fill level by imaging every bottle and finding where the liquid stops. On clear PET and amber bottles, a near-infrared backlight shines through the bottle and the liquid shows up as a dark, high-contrast band. On opaque HDPE, ordinary light can't get through, so the system uses short-wave infrared (SWIR) light around 1,450 nm, which passes through the plastic and is absorbed strongly by water. The choice depends on bottle color and shape. Any bottle outside the fill tolerance set on the HMI is rejected.
Why check every bottle for fill level?
Fillers drift. A nozzle partly clogs, a valve sticks, product temperature or foam changes, and some bottles come out short or over. Sampling a bottle now and then catches a drift only if it lands in the sample.
Overfill matters too. It gives away product on every bottle, and too little headspace can make capping and sealing less consistent. A fill check catches both directions with one measurement.
A short-filled bottle is a net-contents problem: product the plant has to hold, rework or pull back. Checking every bottle at the filler or capper exit keeps short fills from reaching the case packer and points the crew to the filling head that is drifting.
How does a near-IR backlight work on clear and amber bottles?
The light sits behind the bottle and the camera in front, so the camera sees the bottle as a silhouette. Near-infrared light passes through clear PET, and through amber or tinted plastic and glass better than visible light does. Where there is liquid, the light is bent at the surface and absorbed by the product, so the liquid reads as a dark band and the empty headspace above it reads bright[1].
The fill line is the edge between the two. The system measures that edge against the nominal fill height on every bottle.
Why does opaque HDPE need SWIR?
A milky or white HDPE bottle scatters visible and near-IR light, so a standard backlight just shows a glowing bottle with no level in it. Short-wave infrared works differently. Around 1,450 nm, water absorbs strongly, about 1,000 times more than at other common sensing wavelengths, while thin HDPE lets enough of that light through[2][3]. With a SWIR light and a SWIR-capable camera, the water-based liquid inside reads dark against the headspace, even though the bottle looks solid to the eye.
How do bottle color and shape change the setup?
- Clear PET: near-IR backlight, usually the simplest setup.
- Amber or tinted: near-IR backlight, chosen because it gets through the tint.
- Opaque HDPE: SWIR light and camera.
- Shape: on some bottle sizes and shapes, a front light gives a cleaner fill edge than a backlight, for example where the shoulder curves sharply at the fill height. We pick it per bottle.
Foam and a moving meniscus can blur the fill edge on some products, so we test with real product at line speed before we commit to a light.
How is the fill tolerance set?
On the HMI. The plant sets a nominal fill height and a tolerance. The right tolerance depends on the customer and the product, and it is adjustable on the HMI. The tolerance is part of the recipe, so it changes automatically when the plant's MES pushes a changeover over EtherNet/IP[4] or TCP/IP.
A typical strobed exposure is about 60 microseconds[5], short enough to freeze a moving bottle. The speed a given line can run depends on the bottle, the light and the product.
What happens to a bottle that fails?
An encoder-tracked pneumatic reject, driven by a PLC output, removes the exact bottle that failed. Each result is logged with a timestamp and the measured level, so the plant can trace short fills back to the time and the run.
Because every measured level is kept, not just the rejects, the log also shows trends. A level that creeps toward the edge of the tolerance over a shift is visible on the HMI before it turns into a run of rejected bottles, which gives maintenance a chance to look at the filler first.
Operators work from the same JM Automated Solutions HMI as our other systems: live image, pass/fail, false-reject counts and recipe changeover. If the bottle carries a printed code, the same station can read it with deep learning OCR. The system is calibrated against bottles filled to known levels at setup and re-checked at changeover. The hardware is built for washdown areas.
Want to know which light works on your bottles?
Send us a few filled bottles of each type, including some short fills. We'll test them and tell you in writing which lighting gives a reliable fill edge on your line, before any proposal or price. Book a call or send JM Automated Solutions a message.
See the fill level inspection station page for the station setup at a glance.